Fluid machines for compressing fluid or expanding fluid are known in the art. An example of a fluid machine of this type is disclosed in Japanese Published Patent Application No. 2007-239666, for example.
Specifically, Japanese Published Patent Application No. 2007-239666 discloses, as a fluid machine of this type, a compressor for performing two-stage compression of refrigerant. The compressor includes two eccentric rotation mechanisms. Each eccentric rotation mechanism includes compression chambers, one formed on the inner side and the other on the outer side of an annular piston. In a two-stage compression operation in which refrigerant is compressed in two stages, the first compression chamber of the first eccentric rotation mechanism and the second compression chamber of the second eccentric rotation mechanism serve as compression chambers of the lower-stage side, and the third compression chamber of the first eccentric rotation mechanism and the fourth compression chamber of the second eccentric rotation mechanism serve as compression chambers of the higher-stage side. That is, in each eccentric rotation mechanism, one compression chamber serves as a lower-stage compression chamber with the other compression chamber serving as a higher-stage compression chamber.